I created a systemwide OS X service bound to ⇧⌘1 to translate GER-ENG with this ThisService http://wafflesoftware.net/thisservice/ script.

ThisServiceLEO.rb

#!/usr/bin/env ruby

# ThisService Ruby service script example
# Service type: Acts on input.
# Revision 1.

# Unicode considerations:
#  Set $KCODE to 'u'. This makes STDIN and STDOUT both act as containing UTF-8.
$KCODE = 'u'

#  Since any Ruby version before 1.9 doesn't much care for Unicode,
#  patch in a new String#utf8_length method that returns the correct length
#  for UTF-8 strings.
UNICODE_COMPETENT = ((RUBY_VERSION)[0..2].to_f > 1.8)

unless UNICODE_COMPETENT # lower than 1.9
  class String
    def utf8_length
      i = 0
      i = self.scan(/(.)/).length
      i
    end
  end
else # 1.9 and above
  class String
    alias_method :utf8_length, :length
  end
end

input = STDIN.gets nil
# input now contains the contents of STDIN.
# Write your script here.

# LEO
# Raphael Schaad, 2011-02-01

require 'cgi'

url = "http://dict.leo.org/ende?lp=ende&lang=de&searchLoc=0&cmpType=relaxed&sectHdr=on&spellToler=&search="
url += CGI::escape(input)

system("open -a safari '" + url + "'");